1. Field of the Invention
The present invention relates generally to electrochemical devices and, more particularly, to terminal connector assemblies for a device such as a battery. Specifically, the present invention relates to improved terminal assemblies for electrochemical devices, such as batteries, which assembly structures reduce the transmission of mechanical loads to the sealing mechanism thereof. In addition, the present invention further relates to electrochemical cell casing structures adapted to contain such improved terminal assemblies as well as to provide substantial gripping handles for the battery.
2. Description of the Prior Art
A major concern in the manufacture and use of sealed electrochemical devices, such as batteries, is that of leakage of electrolyte and/or gas from the battery container. Under normal conditions, such leakage generally occurs at the site where a battery terminal exits the battery container or casing thus providing a path for leakage. Optimally, a battery terminal should be capable of complete sealing against leakage of electrolyte and/or gases contained within the battery during the lifetime of the battery.
Numerous approaches to resolving this problem have been developed in the past. Such past approaches have included the use of elastic bushings, grommets, press-fit ferrule structures, and the like. A particularly successful battery terminal arrangement is disclosed in U.S. Pat. No. 4,859,547, the contents of which are hereby incorporated herein by reference. This particular arrangement includes a battery terminal post which passes through an opening in a resilient casing, and a pair of ferrules or bushings inserted about the terminal post and press-fit into the opening within the casing wall. In this manner, a much more efficient seal is effected between the terminal post and the plastic casing at the terminal interface without failure due to electrolyte or gas seepage.
Nonetheless, battery terminal structures utilized in existing starved electrolyte recombination batteries do not generally provide adequate gas and electrolyte sealing for a long-life, sealed cell, especially where the terminals are subjected to vibrational stresses. Typically, the battery as designed does provide adequate sealing. However, when mechanical loads, such as torques and pullouts, are applied to the exterior terminal connectors, such mechanical loads are transmitted to the sealing area and tend to loosen the seal. When a seal fails, the life of the battery is diminished through the loss of electrolyte and the ingress of oxygen, as well as through the corrosion of the battery terminal post and the connectors.
In another battery terminal design as taught in U.S. Pat. No. 3,704,173, the seal used in a sealed recombination cell has a terminal seal which prevents the leakage of gas and electrolyte between the lead and plastic parts. This seal depends on an expanding body, that is a rivet, to create and maintain the seal. The external terminal connector of the cell is of a different material from the lead post and also depends on intimate contact between the rivet and the post to obtain a path through which current can flow. An alternate design for the terminals, as disclosed in U.S. Pat. No. 3,964,934, includes the use of a threaded stud which is cast into the post during the post manufacturing. This design depends on the drawing of the stud into the plastic post cavity via a nut to obtain its seal. Both of these designs require non-lead parts to create the electrolyte and gas seal. Additionally, should a corrosion occur between the lead post and the expansion body, that is the rivet or the stud, the electrical contact between the rivet or stud and the lead port can be seriously degraded or lost, thus making the cell unusable. For high-current applications, the dissimilar metals contact creates an area which is susceptible to heating due to contact resistance. This can result in weakening of the seal area and also promotes oxidation of the contact surfaces which can further increase the contact resistance.
The terminal seal taught by U.S. Pat. No. 4,859,547 overcomes some of the aforementioned problems. This particular design permits the use of all lead parts and a terminal configuration without sacrificing seal performance, manufacturing ease or manufacturing costs. Under the design of this particular U.S. Patent, the plastic seal area is molded into the battery lid. However, under vibrational loads and/or high external mechanical stresses, the seal can nonetheless be damaged. Damage can also result to the terminal seal when the battery lid moves relative to the battery elements and the battery case or when the outer terminal moves relative to the sealing components in the battery lid. Thus, there still remains a need for a battery terminal design which provides long-term sealing capability against leakage despite mechanical loading on the battery and which overcomes the other aforementioned problems.